AP_Common: define the ARRAY_SUBSCRIPT macro

libraries/AP_Common/AP_Common.h

@@ -44,6 +44,18 @@
 #define ToRad(x) radians(x)	// *pi/180
 #define ToDeg(x) degrees(x)	// *180/pi
 
+/* Declare and implement const and non-const versions of the array subscript
+ * operator. The object is treated as an array of type_ values. */
+#define ARRAY_SUBSCRIPT(type_) \
+inline type_ &operator[](size_t i) \
+{ \
+    return reinterpret_cast<type_ *>(this)[i]; \
+} \
+inline type_ operator[](size_t i) const \
+{ \
+    return reinterpret_cast<const type_ *>(this)[i]; \
+}
+
 #define LOCATION_ALT_MAX_M  83000   // maximum altitude (in meters) that can be fit into Location structure's alt field
 
 /*